Molecular phylogeny of cetaceans prompts revision of morphological transformations.

The echolocating toothed whales and the filter-feeding baleen whales are traditionally considered as two monophyletic lineages that originated from the extinct cetacean suborder Archaeoceti. While current interpretation of the morphological and behavioural data sets supports toothed-whale monophyly, molecular phylogenies contradict this long-accepted taxonomic subdivision. The molecular data indicate that one group of toothed whales, the sperm whales, Is more closely related to the morphologically highly divergent baleen whales than to other odontocetes. Furthermore, these molecular analyses tentatively suggest a more recent origin of baleen whales than has been generally accepted. Although a thorough cladistic analysis of all relevant morphological data is still needed, reevaluation of some of the most important of these characters helps to reconcile the morphological and the molecular approaches.